1. Field of the Invention
The present invention relates to a lid unit for a thin plate supporting container for housing a thin plate such as a semiconductor wafer, a storage disk, or a liquid crystal glass substrate. The container may be used in storing, transporting, manufacturing and the like.
2. Related Background Art
Containers for housing thin plates such as semiconductor wafers for storage and transport are generally known.
The thin plate supporting container is constructed mainly of a container body and a lid unit for closing the upper opening of the container body. In the container body, a member for supporting thin plates such as semiconductor wafers is provided. Such a thin plate supporting container must be capable of maintaining a clean interior in order to prevent contamination of the surfaces of the thin plates housed inside. Consequently, the container is sealed. To be specific, a lid unit is fixed on the container body to airtightly seal the opening of the container body. Various structures are known for fixing the lid unit on the container body.
The thin plate supporting container transported to a semiconductor manufacturing factory or the like is placed on a manufacturing line and the lid unit is automatically removed by a dedicated apparatus.
An example of a lid unit adapted to such a dedicated apparatus is disclosed in Japanese Patent Application Laid-Open No. 2001-512288 as including, as shown in FIG. 2, a body 2, a cam member 3, a latch arm 4, and a fulcrum 5.
The cam member 3 is rotatably attached to the body 2 and includes a cam portion 6. In the cam portion 6, is a coupling opening 7 having the shape of an arched elongated hole.
At the base end of the latch arm 4, an S-shaped cam follower 8 is provided. The S-shaped cam follower 8 is received and held in the coupling opening 7.
A fulcrum 5 is provided in the form of a projection that supports the latch arm 4.
When the cam member 3 rotates, the S-shaped cam follower 8 in the coupling opening 7 is lifted upward while being moved to the right in the diagram. Consequently, the latch arm 4 swings around the fulcrum 5 while being extended from the body 2 and the tip of the latch arm 4 is pressed downward.
At this time, the tip of the latch arm 4 is inserted into a hole in the container body. By being pressed downward, the tip of the latch arm 4 presses the lid unit against the container body so as to fix the lid unit to the container body.
However, since the base end of the latch arm 4 is lifted upward while being captured by the cam member 3 and extended, in pivoting the latch arm 4 about the fulcrum 5 as a center, in the sense of a lever action, the base end of the latch arm 4 is the power point, and the tip is the point of force application. Accordingly, to press the lid unit 1 strongly against the container body in order to increase air tightness within the container body, it is necessary to strongly press the tip of the latch arm 4 against the rim of the receiving hole or recess in the container body. For this purpose, the strength of the cam member 3 and the latch arm 4 must be increased to allow for an increase in the distance between the tip of the latch arm 4 and the fulcrum 5.
On the other hand, by moving the fulcrum 5 toward the tip of the latch arm 4, the tip of the latch arm 4 can be more strongly pressed against the rim of the hole in the container body side without increasing the strength of the cam member 3 and the latch arm 4. However, when the fulcrum 5 is moved toward the tip side, the distance through which the base end of the latch arm 4 is lifted upward becomes longer. If the distance to lift is thus increased, a problem occurs in that the lid unit 1 must be made thicker.
On the inner face of the lid unit, a wafer presser is usually provided. The wafer presser supports semiconductor wafers housed in the container body by pressing the semiconductor wafers from above. As the diameter of a semiconductor wafer increases, the support for the semiconductor wafer must also be increased. Accordingly, reactive force from the semiconductor wafer which is received by the wafer presser increases. Also, as the number of housed semiconductor wafers increases, reactive force from the semiconductor wafers increases. As a result, the lid unit and the wafer retainer are outwardly deflected whereby the pressing force in the center portion of the wafer presser is weakened and, if vibration is received from the outside, the semiconductor wafers rotate (cant).